Natural three-dimensional vision is produced by each eye perceiving the image of the objects from a view point slightly different from that of the other eye of a specific person, allowing depths and reliefs to be perceived, after the corresponding integrating and processing of the images in said person's brain.
Different systems in order to adapt three-dimensional images previously registered in a special way, and which try to imitate natural three-dimensional vision, are known.
Since photography and cinematography have come into existence, an infinite number of ways to reproduce and view three-dimensional images has been sought.
The simplest systems consist of taking two simultaneous photographs of a single object from slightly different angles, so that the two lenses of the corresponding cameras have a separation equivalent to that between a person's eyes. Subsequently, once the two photographs are developed they are placed on a plane with an opaque barrier perpendicular to said plane and the viewer brings his face towards this barrier in such a way that his right eye only sees the photograph that corresponds to it and his left eye only sees the other photograph, thus obtaining the three-dimensional effect.
Anaglyphs, that are produced by means of printing stereographs in the form of superimposed images of two complementary colors, for example, red and green, are known. For three-dimensional vision, some glasses with filters of said two colors are used, each one of them over each eye, so that each eye only sees the stereo image that corresponds to it.
On the other hand, there are systems of polarized light in which two beams are projected on a screen, one of them polarized vertically and the other one polarized horizontally, thanks to some filters coupled to the projection lenses. The viewers have to wear polarized glasses whose planes are oriented in such a way that each eye receives only the image that corresponds to it. An example of another system based on polarization is disclosed in EP-A-0233636.
There are also autostereoscopic three-dimensional viewing means, which are those in which the viewer does not need any complementary glasses or viewing device. Among these methods are holographs, which are photographic techniques which use laser light; magic images which are those in which the image is broken down and the three-dimensional effect appears before a specific focus by the viewer; and parallactic stereograms which is the system that is the most similar to the present invention.
In parallactic stereograms, a grating of lines or traces in contract to the emulsion acts as a mask, allowing separate registering of the left and right images as a series of vertical lines. The positive transparency is projected on the screen through a similar grating, in such a way that each eye only sees the appropriate image. A normal grating produces the loss of a large amount of light (805), therefore, almost all the modern systems use gratings formed by cylindrical and fine lenses. Parallactic systems are disclosed in, for example, JP-A-2-14697 and EP-A-262955.